Our time,their time,world time: The transformation of temporal modes*

This article discusses Protestant movements in a village in the Peruvian Andes. It tries to explain why villagers either reject or are attracted to Protestantism. The argument is that explanations traditionally proposed by anthropologists fail to account for the segmentation into competing denominations, the problem of relapse to Catholicism, and second‐ and third‐time conversion, and that new approaches are required to understand the nature of contemporary Protestant movements in Latin America. The article concludes that we enlarge our framework to include urban migrants and focus on the ties which link these migrants to their native village.     

Population structure attributable to reproductive time: isolation by time and adaptation by time

Many populations are composed of a mixture of individuals that reproduce at different times, and these times are often heritable. Under these conditions, gene flow should be limited between early and late reproducers, even within populations having a unimodal temporal distribution of reproductive activity. This temporal restriction on gene flow might be called "isolation by time" (IBT) to acknowledge its analogy with isolation by distance (IBD). IBD and IBT are not exactly equivalent, however, owing to differences between dispersal in space and dispersal in time. We review empirical studies of natural populations that provide evidence for IBT based on heritabilities of reproductive time and on molecular genetic differences associated with reproductive time. When IBT is present, variation in selection through the reproductive season may lead to adaptive temporal variation in phenotypic traits [adaptation by time (ABT)]. We introduce a novel theoretical model that shows how ABT increases as (i) selection on the trait increases; (ii) environmental influences on reproductive time decrease; (iii) the heritability of reproductive time increases; and (iv) the temporal distribution of reproductive activity becomes increasingly uniform. We then review empirical studies of natural populations that provide evidence for ABT by documenting adaptive temporal clines in phenotypic traits. The best evidence for IBT and ABT currently comes from salmonid fishes and flowering plants, but we expect that future work will show these processes are more widespread.     

Memory time

In this issue of Neuron, MacDonald et al. describe hippocampal "time cells" that fire during specific delay periods as rats performed a memory task. Converging results in monkeys suggest that the hippocampus encodes episodes by signaling events in time.     

Mapping time

Neuronal coding of temporal stimulus features can occur by means of delay lines. Given that neuronal activity is conducted through many parallel axons, there has to be a mechanism guaranteeing minimal temporal dispersion. We argue that plastic changes in synaptic transmission that are unspecifically propagated along presynaptic axons are a basis for the development of delay-line topologies. Furthermore, we show how two populations of afferents form a map of interaural time differences as found, for instance, in the laminar nucleus of the barn owl.     

The dual klepsydra model of internal time representation and time reproduction

We present a model of the internal representation and reproduction of temporal durations, the 'dual klepsydra' model (DKM). Unlike most contemporary models operating on a 'pacemaker-counter' scheme, the DKM does not assume an oscillatory process as the internal time-base. It is based on irreversible, dissipative processes in inflow/outflow systems (leaky klepsydrae), whose states are continuously compared; if their states are equal, durations are subjectively perceived as equal. Model-based predictions fit experimental time reproduction data with good accuracy, and show qualitative features not accounted for by other models. The deterministic model is characterized by two parameters, kappa (outflow rate coefficient) and eta (ratio of inflow rates). A stochastic version of the model (SDKM) assumes randomly fluctuating inflows, involves two more parameters, and accounts for intra-individual variance of reproduced durations. Analysis of the SDKM leads to non-trivial problems in the stochastic theory, briefly sketched here. Methods of parameter estimation for both deterministic and stochastic versions are given. Applying the DKM to the subjective experience of time passage, we show how subjective measure of elapsed time is constituted. Finally, essential features of the model and its possible neurophysiological interpretation are discussed.     

It's time to flower: the genetic control of flowering time

In plants, successful sexual reproduction and the ensuing development of seeds and fruits depend on flowering at the right time. This involves coordinating flowering with the appropriate season and with the developmental history of the plant. Genetic and molecular analysis in the small cruciform weed, Arabidopsis, has revealed distinct but linked pathways that are responsible for detecting the major seasonal cues of day length and cold temperature, as well as other local environmental and internal signals. The balance of signals from these pathways is integrated by a common set of genes to determine when flowering occurs. Excitingly, it has been discovered that many of these same genes regulate flowering in other plants, such as rice. This review focuses on recent advances in how three of the signalling pathways (the day-length, vernalisation and autonomous pathways) function to control flowering.